Newsgroups: comp.robotics
Path: brunix!uunet!destroyer!gatech!taco!news
From: wglee@ecerl3.ece.ncsu.edu (William Gary Lee)
Subject: laser range finder
Message-ID: <1992Oct28.224337.19610@ncsu.edu>
Sender: news@ncsu.edu (USENET News System)
Organization: North Carolina State University, Raleigh
Date: Wed, 28 Oct 1992 22:43:37 GMT
Lines: 45

Hello,

I'm working on a project that requires the development of a laser range
finder for a mobile robot (Cybermation KMA). I want to build a scanning
range finder that determines distance based on time-of-flight;
detectable ranges should be in the range of 1 meter to 20+ meters.
 
For time-of-flight systems, range is determined by evaluating the phase
shift between the reference & reflected portions of an amplitude-modulated
CW laser beam. At one meter there will be a six nanosecond time delay in
the reflected beam and at 20 meters there will be a 120 nanosecond
delay. I have considered basing the design on a digital-counter
approach, but *minimum* sampling frequency would be 700 MHz which is
pushing the envelope for even the fastest ECL devices of which I am aware.
I guess I will have to take an analog approach (something along the
lines of conventional radar), but I don't have any good leads for
reference material.

My questions are:

1) Any suggestions regarding a good analog (or digital) approach to
detecting very small phase shift.

2) I've heard phase-locked loops and heterodyne systems are based on
phase-shift detection but have no knowledge of same. Any suggestions for
good intro texts if these methods seem promising?

3) I know Peripheral Systems (?) and Environmental Research Institute of
Michigan have done some work in this area but haven't seen any
publications that would include schematics for the phase-shift detector.
Does anyone have a working knowledge of these systems (nothing
proprietary of course)?

Any help in these matters would be much appreciated.

          +++++++++++++++++++++++++++++++++++++++++++++++++++++
	 /	Gary Lee				       \
	*       Center for Robotics and Intelligent Machines    *
	*       Electrical and Computer Engineering Dept.	*
	*       North Carolina State University			*
	*	Raleigh, NC 					*
	*							*
	*	email: wglee@eceris.ece.ncsu.edu		*
	*-------------------------------------------------------*
       /=========================================================\  
